1. Field of the Invention
The present invention relates to a multi-optical axis photoelectric sensor forming a light curtain for detecting a human body and the like penetrating into a predetermined area. In more detail, the present invention relates to an output of the multi-optical axis photoelectric sensor provided for a non-safety control device.
2. Description of the Related Art
In general cases, a multi-optical axis photoelectric sensor for detecting a human body and the like, is utilized where a person can come in contact with a hazardous source, thereby providing safety to the person in view of a machine which is assessed as the hazardous source such as a press machine. The multi-optical axis photoelectric sensor includes: an emitting unit having a plurality of emitting elements arranged in a line; and a receiving unit having a plurality of receiving elements which receive light beams from the plurality of emitting elements and arranged in a line. A light curtain is formed by a plurality of light beams between the emitting unit and the receiving unit, to separate the hazardous source from the other area. In case where an object penetrates into the light curtain, the multi-optical axis photoelectric sensor detects that the light beam is intercepted (blocked). In this case, the multi-optical axis photoelectric sensor outputs a cutout signal for cutting out a power supply to a motor and the like which drives the hazardous source.
The multi-optical axis photoelectric sensor including various kinds of special functions has been developed. This is shown, for example, in Japanese published patent No. 2003-218679. The special functions are, for example, a muting function, an override function etc. as described below.
The “Muting function” is a function to temporarily disable the detection function of the multi-optical axis photoelectric sensor in response to a signal received (“muting signal”, hereinafter) from an external muting sensor. When the muting function is activated, the multi-optical axis photoelectric sensor temporarily provides a safety control signal representing an operation allowable even if the light beam is blocked. In detail, the safety control signal representing the operation allowable is ON state signal.
A photoelectric sensor and a limit switch are suitable for the muting sensor. A status of the multi-optical axis photoelectric sensor is shifted to a status in which the muting function is activated (“muting status”, hereinafter) when a condition regarding the multi-optical axis photoelectric sensor meets the requirement that all of the light beams of the multi-optical axis photoelectric sensor pass through in a normal mode (normal operating status), namely the safety control signal is ON state, and the muting signal is received. On the other hand, when the condition regarding the multi-optical axis photoelectric sensor does not meet the requirement, for example, a) one of any light beams is intercepted in the normal mode, namely the safety control signal is OFF state or b) an abnormal status is detected by a self check function of the multi-optical axis photoelectric sensor, a shifting into the muting status is not performed even if the muting signal is received.
The multi-optical axis photoelectric sensor has the self check function for watching fault itself, an abnormal condition from external noises etc. all the time. In case where at least one fault and some abnormal condition is detected by the self check function, a safety control signal representing an operation non-allowable is provided even if all of the light beams for detecting the object are passed through. In some cases, a product line is suspended when a product machine is cut off based on the safety control signal representing an operation non-allowable signal. In such a case, productivity may decrease. On the other hand, the multi-optical axis photoelectric sensor outputs the safety control signal representing an operation non-allowable signal in accordance with an improper user's operation for setting an additional function such as the muting function since the multi-optical axis photoelectric sensor is developed under the fail safe concept.
Referring to FIG. 5, an example of system installing the muting function will be described.
In FIG. 5A, a robot 101 and a processing machine M are disposed in an area surrounded by protective fences. The protective fences have an opening for a path passed by an operator O who carries an object W into the area. The emitting unit 2 and the receiving unit 3 are placed in front of the opening. Consequently, the light curtain, namely a detection area A, is formed corresponding to the opening in order to detect the operator O existing at the opening of the protective fences.
As shown in FIG. 5B, a rotating motion of an arm 102 is locked by a rod 105 of a cylinder 104 when the emitting unit 2 and the receiving unit 3 of the multi-optical axis photoelectric sensor does not detect an operator O penetrating into the detection area A. Then, the lock status is detected by, for example, an optical sensor 110. The optical sensor 110 is connected to a muting input terminal of the multi-optical axis photoelectric sensor. Thus, the status of the multi-optical axis photoelectric sensor is shifted to muting status based on the muting signal from the optical sensor 110. Consequently, the operator O is permitted to enter the detection area A to carry the object W on a rest 100.
The robot 101 rotates the arm 102, and provides the object W disposed on the rest 100 in an operation area, and the robot 101 carries it to a processing machine M. The robot 101 is able to rotate only when the rod 105 of the cylinder 104 equipped at a rotating unit 103 as shown in FIG. 5D is located downwardly. The robot 101 is not allowed to rotate in the case of FIG. 5B. Therefore, safety for the operator O in the detection area A is secured although the operator O is located in the detection area A.
In case of restarting of the robot 101 to operate, as shown in FIG. 5C, the operator O goes out from the detection area A and pushes a start button 107 of an operational panel 106. Consequently, the rod 105 moves downwardly as shown in FIG. 5D. Therefore, the muting status is canceled since a requirement for maintaining the muting status is not met based on passing through of the optical sensor 110. In this case, the arm 102 shown in FIG. 5C rotates and puts the object W on the rest 100.
However, for example, in case where the operator O does not exit from the detection area A completely and reaches for the start button 107, a careless stop occurs in that part of the industrial system since the muting status is canceled and the light beam is stilt intercepted by the operator O.
When the multi-optical axis photoelectric sensor detects the object on the light curtain, the safety control signal becomes OFF state. This status is an interlock status. There are two ways to return from the interlock status to the normal operating status.
One way is to automatically reset; that is, a requirement for returning to the normal operating status is that all light beams passed through.
The other way is to manually reset; that is, a requirement for returning to the normal operating status is not only that all light beam are passed through, but also that an interlock reset signal is provided. In the case of an interlock by manually reset, an operator pushes an interlock reset button to reset the interlock of the multi-optical axis photoelectric sensor. However, the operator can not know whether the multi-optical axis photoelectric sensor has been prepared for receiving the interlock reset signal or not. The operator does not know whether the interlock was reset or not, either.
To control the multi-optical axis photoelectric sensor via a non-safety controller, such as a PLC (Programmable Logic Controller) may solve these problems, but safety regulations may not permit one to control the safety component via a non-safety controller. Thus, these problems still remain.